From e20f5f34ea3e65645803908869a153830c597e89 Mon Sep 17 00:00:00 2001
From: Dominatorrr <276074461+Pllutonyy@users.noreply.github.com>
Date: Fri, 18 Sep 2026 17:29:31 +0300
Subject: [PATCH] fix(cursor): preserve native Claude effort model IDs before
 executor dispatch (#12838)

---
 docs/providers/CURSOR-API-KEY-AND-CLI.md      | 16 ++++++-
 .../handlers/chatCore/claudeEffortVariant.ts  | 11 +++++
 .../chatcore-claude-effort-variant.test.ts    | 42 +++++++++++++++++++
 3 files changed, 67 insertions(+), 2 deletions(-)

diff --git a/docs/providers/CURSOR-API-KEY-AND-CLI.md b/docs/providers/CURSOR-API-KEY-AND-CLI.md
index 53c0a85dfd..8449882947 100644
--- a/docs/providers/CURSOR-API-KEY-AND-CLI.md
+++ b/docs/providers/CURSOR-API-KEY-AND-CLI.md
@@ -1,7 +1,7 @@
 ---
 title: "Cursor API provider and the Cursor CLI passthrough"
-version: 3.8.50
-lastUpdated: 2026-08-19
+version: 3.8.51
+lastUpdated: 2026-09-05
 ---
 
 # Cursor API provider and the Cursor CLI passthrough
@@ -66,6 +66,18 @@ Notes:
 - `POST /api/providers/{id}/refresh-cursor` is for the `cursor` IDE provider
   only; `cursor-api` connections have no IDE session to renew.
 
+## Native model IDs and effort
+
+For `cursor` / `cu` and `cursor-api` / `cua`, the shared Claude-effort normalizer
+leaves the requested model ID intact. Cursor can advertise a suffix such as
+`-low` as part of a real model ID, rather than as an OmniRoute effort alias.
+The Cursor executor preserves an exact live-catalog match; when there is no
+match, its existing model resolver owns suffix-to-parameter fallback.
+
+This does not change effort normalization for direct Claude, Claude-compatible,
+or Vertex routes. Availability still depends on the selected Cursor account's
+catalog and entitlement.
+
 ## Cursor CLI passthrough
 
 Route: `src/app/api/cursor-cli/[...path]/route.ts` →
diff --git a/open-sse/handlers/chatCore/claudeEffortVariant.ts b/open-sse/handlers/chatCore/claudeEffortVariant.ts
index dac50233ad..2da837a4f6 100644
--- a/open-sse/handlers/chatCore/claudeEffortVariant.ts
+++ b/open-sse/handlers/chatCore/claudeEffortVariant.ts
@@ -38,6 +38,17 @@ export function applyClaudeEffortVariant(opts: {
   sourceFormat: string;
 }): { effectiveModel: string; log: string | null } {
   const { provider, body, sourceFormat } = opts;
+  // Cursor advertises native effort-suffixed ids. Its executor resolves exact
+  // live-catalog ids before applying its own suffix fallback; stripping here
+  // destroys that information before the executor can see it.
+  if (
+    provider === "cursor" ||
+    provider === "cu" ||
+    provider === "cursor-api" ||
+    provider === "cua"
+  ) {
+    return { effectiveModel: opts.effectiveModel, log: null };
+  }
   let effectiveModel = opts.effectiveModel;
   let log: string | null = null;
 
diff --git a/tests/unit/chatcore-claude-effort-variant.test.ts b/tests/unit/chatcore-claude-effort-variant.test.ts
index 0630a3c7bd..4cda1b2a47 100644
--- a/tests/unit/chatcore-claude-effort-variant.test.ts
+++ b/tests/unit/chatcore-claude-effort-variant.test.ts
@@ -10,6 +10,48 @@ import { test } from "node:test";
 import assert from "node:assert/strict";
 import { applyClaudeEffortVariant } from "../../open-sse/handlers/chatCore/claudeEffortVariant.ts";
 import { FORMATS } from "../../open-sse/translator/formats.ts";
+import { resolveRequestedModel } from "../../open-sse/utils/cursorAgentProtobuf.ts";
+
+for (const provider of ["cursor", "cu", "cursor-api", "cua"]) {
+  for (const sourceFormat of [FORMATS.OPENAI, FORMATS.CLAUDE, FORMATS.OPENAI_RESPONSES]) {
+    test(`${provider}/${sourceFormat}: preserves native Cursor Claude model ids before executor resolution`, () => {
+      for (const model of [
+        "claude-fable-5-1-low",
+        "claude-fable-5-1-thinking-low",
+        "claude-opus-5-low",
+      ]) {
+        const body = { model, messages: [] };
+        const result = applyClaudeEffortVariant({
+          provider,
+          effectiveModel: model,
+          body,
+          sourceFormat,
+        });
+        assert.deepEqual(result, { effectiveModel: model, log: null });
+        assert.deepEqual(body, { model, messages: [] });
+        assert.deepEqual(
+          resolveRequestedModel(result.effectiveModel, { liveCatalogIds: new Set([model]) }),
+          { modelId: model, parameters: [] }
+        );
+      }
+    });
+  }
+}
+
+test("Cursor preserves explicit client effort while its encoder owns non-catalog suffix fallback", () => {
+  const body = { model: "claude-opus-5-low", reasoning_effort: "none", messages: [] };
+  const result = applyClaudeEffortVariant({
+    provider: "cursor",
+    effectiveModel: body.model,
+    body,
+    sourceFormat: FORMATS.OPENAI,
+  });
+  assert.deepEqual(body, { model: "claude-opus-5-low", reasoning_effort: "none", messages: [] });
+  assert.deepEqual(resolveRequestedModel(result.effectiveModel, { liveCatalogIds: new Set() }), {
+    modelId: "claude-opus-5",
+    parameters: [{ id: "effort", value: "low" }],
+  });
+});
 
 test("claude provider + effort suffix → strips to base, mutates body model + reasoning_effort, returns log", () => {
   const body: Record<string, unknown> = { model: "claude-sonnet-4-high", messages: [] };